In the International Deep Brain Stimulation Database and Registry, the average total Yale Global Tic Severity Scale (YGTSS) score for Tourette syndrome patients improved from 75.01 to 41.19 one year after DBS implantation, Michael Okun, MD, of the University of Florida in Gainesville, and colleagues reported online in JAMA Neurology.

Motor tic subscores improved from an average of 21.00 to 12.97 and phonic tic subscores improved from 16.82 to 9.63 in that period, they added. Side effects occurred in 35.4% of patients, most frequently dysarthria (6.3%) and paresthesia (8.2%).

"The majority of patients with Tourette syndrome don't need surgery, but there are a group of patients with very severe symptoms -- people who can't function, hold a job, go to school, or have normal relationships -- and this could be a valuable therapy for them," he added.

The FDA has not approved DBS for Tourette syndrome, but it is cleared for essential tremor and select cases of Parkinson's disease. FDA also has granted DBS a humanitarian device exemption for dystonia and obsessive-compulsive disorder.

Only a handful of DBS surgeries are performed on Tourette syndrome patients each year at any one center, Okun noted, and many insurance companies do not cover it. Because of those low numbers, DBS centers formed the International Deep Brain Stimulation Database and Registry in 2012 to share data. Registry members launched a public website this week to track future outcomes of all participating institutions.

The registry analysis included data from 185 patients who had DBS for Tourette syndrome at 31 different institutions throughout Australia, Europe, Asia, and North America from 2012 to 2016. Participants had been selected for surgery based on local evaluations. Inclusion criteria were not standardized.

Although 185 individuals were included in the sample, not every site collected each data point. The researchers had complete information for 89 patients to determine total YGTSS scores. For motor and phonic tic subscores, they had complete data for 40 participants each.

Of 171 participants with available data, 78.4% were male, with a mean age of symptom onset of about 8 years. The average age at diagnosis was 12 and the average age at surgery was 29.

The two most common comorbidities were obsessive-compulsive disorder, which affected 64.2% of patients, and depression, which affected 47.3%. More than a quarter of the group (28.3%) had attention deficit/hyperactivity disorder and 21.6% had a history of self-injurious behavior.

The most commonly targeted brain structure was the centromedian (CM) thalamic region at 57.1%, followed by the anterior globus pallidus internus (GPi) at 25.2%, the posterior GPi at 15.3%, and the anterior limb of the internal capsule (ALIC) at 2.5%.

The pooled 1-year outcomes of the registry showed an improvement of 45.1% in the YGTSS total score, with multiple brain targets producing similar tic suppression.

The overall adverse event rate at one year was 35.4%. Intracranial hemorrhage occurred in two patients (1.3%), infection occurred in four patients with five events (3.2%) and one patient (0.6%) had the DBS device removed. No deaths were reported. The most common side effects were dysarthria at 6.3% and paresthesia at 8.2%.

While this study improves understanding of adverse event risks and tic reduction efficacy, more work is needed, said Donald Gilbert, MD, MS, of Cincinnati Children's Hospital Medical Center in Ohio, who was not involved in the study.

"The study design is not rigorous enough to form the basis of a standard treatment guideline for severe Tourette Syndrome, and the data leave unanswered questions about more global changes in the patients' day-to-day function," he told MedPage Today.

The international group's consensus recommendations from 2015 -- that DBS be offered only by experienced centers after evaluation by multidisciplinary teams -- remain the best clinical practice, Gilbert added.

Okun and colleagues noted that their analysis is based on an observational, descriptive, open-label study from multiple sites which limits its findings. They had no standard inclusion criteria and could not evaluate the potential effects of medications on outcomes. Some sites may have used different surgical techniques, which may have affected results. Imaging data were not available to correlate outcomes with DBS targeting, and the numbers of each target were skewed with more CM thalamic region and anterior GPi cases.

Okun reported that he was a principal investigator or co-investigator for several National Institutes of Health, foundation, and industry-sponsored trials without receiving honoraria. His institution received support from Medtronic, Abbvie, Allergan, and Abbott/St Jude, but he reported no financial interest in these grants. Co-author Leckman disclosed relationships with Tasly Pharmaceuticals and Grifols LLC. No other industry relationships were reported.

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